A PIC is a device that integrates multiple photonic circuit elements, analogous to electronic integrated circuits. PICs are distinct from electronic integrated circuits in that they use light rather than electrons to carry out a variety of optical functions. PICs allow optical systems to be made more compact, more efficient, more capable, and less expensive than with discrete optical components. PICs are often found in optical communication systems and photonic computing systems, where demand for high-speed and high-bandwidth circuits is ever increasing. The need for denser, more complex PICs grows with the demand for speed and bandwidth. Low-loss photonic circuit elements, such as self-imaging crossings and diffractive beam propagation crossings, allow these demands to be met in a wide variety of devices, including photonic switches, adaptive filters, multi-carrier transceivers, modulators, multiplexers, and demultiplexers, among many others.
PICs generally include multiple optical waveguides and are fabricated from a variety of materials, including silicon, silica, lithium niobate (LiNbO3), gallium arsenide (GaAs), indium phosphide (InP), lead lanthanum zirconate titanate (PLZT), and silicon nitride (Si3N4). For example, in silicon optical waveguides, a typical structure includes a silicon core having a high refractive index surrounded by silicon dioxide (silica) cladding having a low refractive index, which is typically fabricated on a silicon wafer. This structure is common for communication wavelengths, such as the 1310 nm band, the 1490 nm band, and the 1550 nm band. A PIC can be formed by lithographic techniques, including optical lithography and electron-beam lithography. Optical proximity correction techniques can be used to enhance the optical lithography to improve the fabrication precision of photonic circuit elements by more accurately creating the desired element shapes in the PIC material.